Why do the religious people get so up in arms about evolution?

This is a serious question and I'm not here to get converted. I also don't want this to turn into an evolution/creationism debate. I believe what I believe and I am comfortable with you guys believing what you believe but why does this always turn into a fight? Personally, I feel offended and the need to defend myself when confronted but the creationists really take it to heart. This is not meant to be a fight, rather a friendly debate so please keep preaching and nastiness aside.